1. Field of the Invention
The invention relates to a laser welding method that is suitable for joining plural workpieces by welding with a laser beam.
2. Description of Related Art
A laser welding method has widely been used as a method for joining plural metallic workpieces in a state that the workpieces are stacked or abutted. Welding by the laser welding method has the following advantages: less process distortion, capability of high-speed welding, a smaller portion that is influenced by residual heat, and the like.
As such a technique, for example, Japanese Patent Application Publication No. 2013-132686 (JP 2013-132686 A) suggests a laser welding method for joining workpieces that are formed of stacked plural steel sheets. Here, a laser beam is projected onto the workpieces to join the workpieces such that a weld section composed of plural nuggets is formed, so as to join a workpiece W1.
More specifically, as shown in FIG. 10A, the laser beam is projected onto irradiation regions P1 to P3 that are in the same shape and located on a closed curve D such that each of the nuggets is formed along a circumference that is a virtual closed curve D. It is possible to increase reliability of welding of the workpieces by adopting such a laser welding method.
As indicated in JP 2013-132686 A, when a weld section Y that includes nuggets N1 to N3 is formed, the nuggets N1, N2, N3 are sequentially formed. However, as the nuggets N1, N2, N3 are sequentially formed, as shown in FIG. 10B, size of the nugget tends to increase in an order of the nuggets N1 to N3. Consequently, there is a case where the weld section Y in a stable shape cannot be obtained. In particular, such a phenomenon is even more prominent in the case where a large number of the nuggets are sequentially formed in the vicinity of each other or where it is intended to sequentially form the plural nuggets at a high speed.